Photochemical Addition Reactions in the Benzo(b)Thiophene, Benzo(b)Furan, and Indole Series

Abstract

Benzo(b)thiophene (1), benzo(b)furan (2), and indole (3) are a group of fused aromatic heterocyclic compounds related to naphthalene.(1) All are natural products. Benzo(b)thiophene* was discovered by Boes(2) and represents as much as 12%–15% of the sulfur content of the crude naphthalene fraction of some coal tars. It has also been isolated in various oil shales.(3) Benzo(b)furan, called coumarone in older literature, is also found in coal tar and was synthesized first by Fittig and Ebert.† Benzo(b)furan derivatives have many pharmacodynamic applications including use as pesticides, bactericides, and antibiotics. A major group of natural benzo(b)furans, the furocoumarins, are used as skin photosensitizers. Psoralens are particularly active, with 8-methoxypsoralen being used in many suntan lotions and in skin dyes—particularly in Middle Eastern countries.